Back pain is a common human ailment. In fact, approximately 50% of persons who are over 60 years old suffer from lower back pain. Although many incidences of back pain are due to sprains or muscle strains which tend to be self-limited, some back pain is the result of more chronic fibromuscular, osteoarthritic, or ankylosing spondolytic processes of the lumbosacral area. Particularly in the population of over 50 year olds, and most commonly in women, degenerative spine diseases such as degenerative spondylolisthesis (during which one vertebra slides forward over the top of another vertebra) and spinal stenosis (during which the spinal canal markedly narrows) occurs in a high percentage of the population. Iida, et al, 1989.
Degenerative changes of the adult spine have traditionally been determined to be the result of the interrelationship of the three joint complex: the disk and the two facet joints. Degenerative changes in the disc lead to arthritic changes in the facet joint and vice versa. See Farfan and Sullivan, 1967; see also Farfan, 1969; see also Farfan, 1980.
One cadaver study of nineteen cadavers with degenerative spondylolisthesis showed that facet degeneration was more advanced than disc degeneration in all but two cases. Farfan. In mild spondylolisthetic cases, the slip appeared to be primarily the result of predominantly unilateral facet subluxation. Other studies into degenerative changes of the spine have revealed extensive contribution of facet joint degeneration to degenerative spinal pathologies such as degenerative spondylolisthesis, central and lateral stenosis, degenerative scoliosis (i.e., curvature of the spine to one side), and kypho-scoliosis, at all levels of the lumbar spine. See Kirkaldy-Willis et al, 1978; see also Rosenberg, 1975.
It has been determined that facet joint degeneration particularly contributes to degenerative spinal pathologies in levels of the lumbar spine with sagittally oriented facet joints, i.e. the L4-L5 level.
When intractable pain or other neurologic involvement results from adult degenerative spine diseases, such as the ones described above, surgical procedures may become necessary. Traditionally, the surgical management of disease such as spinal stenosis consisted of decompressive laminectomy alone. Herkowitz, et al, The Diagnosis and Management of Degenerative Lumber Spondylolisthesis, 1998. Wide decompressive laminectomies remove the entire lamina, and the marginal osteophytes around the facet joint. Because a lot of degenerative spine disease has been demonstrated to be caused by facet joint degeneration or disease, this procedure removes unnecessary bone from the lamina and insufficient bone from the facet joint.
Furthermore, although patients with one or two levels of spinal stenosis tend to do reasonably well with just a one to two level wide decompressive laminectomy, patients whose spinal stenosis is associated with degenerative spondylolisthesis have not seen good results. Lombardi, 1985. Some studies reported a 65% increase in degree of spondylolisthesis in patients treated with wide decompressive laminectomy. See Johnson et al; see also White and Wiltse. The increase in spinal slippage especially increased in patients treated with three or more levels of decompression, particularly in patients with radical laminectomies where all of the facet joints were removed.
To reduce the occurrence of increased spondylolisthesis resulting from decompressive laminectomy, surgeons have been combining laminectomies, particularly in patients with three or more levels of decompression, with multi-level arthrodesis, which surgically fuses the facet joints to eliminate motion between adjacent vertebrae. Although patients who undergo concomitant arthrodesis do demonstrate a significantly better outcome with less chance of further vertebral slippage after laminectomy, arthrodesis poses problems of its own. Aside from the occurrence of further spondylolisthesis in some patients, additional effects include non-unions, slow rate of fusion even with autografts, and significant morbidity at the graft donor site. Furthermore, even if the fusion is successful, joint motion is totally eliminated at the fusion site, creating additional stress on healthy segments of the spine which can lead to disc degeneration, herniation, instability spondylolysis, and facet joint arthritis in the healthy segments.
An alternative to spinal fusion has been the use of an invertebral disc prosthesis. There are at least 56 artificial disc designs which have been patented or identified as being investigated. McMillin C. R. and Steffee A. D., 20th Annual Meeting of the Society for Biomaterials (abstract) (1994). Although different designs achieve different levels of success with patients, disc replacement mainly helps patients with injured or diseased discs; disc replacement does not address spine pathologies such as spondylolisthesis and spinal stenosis caused by facet joint degeneration or disease.